(a) Technical Field
The present invention relates to a power transmission device for a hybrid vehicle. More particularly, the present invention relates to a power transmission device for a hybrid vehicle, which provides a high damping force against engine fluctuation at low RPM operation by an engine and has an effective layout in terms of driving performance at low RPM by the engine and in terms of NVH (noise, vibration and harshness).
(b) Background Art
In general, a power transmission device for a hybrid vehicle has a layout in which an automatic transmission, a motor, an engine and an integrated starter-generator (ISG) are arranged in a row.
In the hybrid vehicle using the engine and the motor, the motor which is efficient at a low RPM is used for initial acceleration. When the vehicle reaches a predetermined speed, a generator that has the function of a starter motor, i.e., the ISG, starts the engine, and the outputs of the engine and the motor are used simultaneously.
At this time, in order to integrally use the output of the engine and the output of the motor using energy generated by the ISG, the vehicle has a structure in which each of the outputs is connected to one unit of a planetary gear, not depicted, of the automatic transmission.
That is, the engine is connected to a carrier of the planetary gear, the ISG is connected to a sun gear of the planetary gear, and the motor is connected to a ring gear.
Accordingly, rotational power of the engine is adjusted to an appropriate speed in the planetary gear of the automatic transmission, then transferred to a drive shaft, and finally transferred to a drive wheel through a propeller shaft.
At the same time, the ISG connected to the sun gear of the planetary gear in the automatic transmission receives the rotational power from the engine and generates electricity during deceleration. The electricity generated by the ISG is charged to a charger through an inverter, not depicted, and then the inverter supplies electricity to the motor for rotating the drive shaft during vehicle startup or acceleration.
Since the power transmission device for a hybrid vehicle has a structure in which the automatic transmission, the motor, the torque converter, the engine and the ISG are arranged in a row, the overall length of the engine room is increased, and thus it is disadvantageous in terms of the layout and mounting of the respective components. Moreover, it is difficult to commonly apply such a power transmission device to a plurality of different platforms. Accordingly, extensive research aimed at developing a power transmission device which is advantageous for mass production and has an optimal layout has continued to progress.
For conventional power transmission devices for a hybrid vehicle, a primary inertia in front of a damper spring of the device has a limited structure, the driving performance at a low RPM is degraded.
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.